A preliminary feasibility study reported in this proposal suggests that a specific form of dynamical instability may result in the paroxysmal discharge antecedent to focal epileptic seizures. This behavior has been termed "deterministic chaos" and can be exhibited by differential equations including those that describe simple feedback circuits. The type of solution exhibited by a differential equation is not fixed. The same equation may display transitions between steady state, periodic or caotic motion as the result of small changes in the numerical values of constant parameters. Analogous parameter dependent transitions have been observed experimentally in electronic circuits, chemical reactions and during the transition to turbulent fluid flow. The proposed investigation considers a restricted problem: can neural systems enter regions of chaotic behavior? An initial goal is the prediction of parameter values (drug concentrations and ionic environments) that could result in chaotic neural output. A precise knowledge of the dependence of dynamical behavior on parameters that can be regulated pharmacologically may identify procedures for effecting a reverse transition from chaos to the normal state. A systematic mathematical investigation is essential because the large number of independent parameters make immediate recourse to trial and error animal experimentation unacceptably slow and expensive.